Driver side airbags are conventionally mounted on steering wheels along with horn blowing switch arrangements. Thin membrane type horn switches provide an advantage in such airbag module assemblies because such a switch can be readily mounted directly on the module cover and actuation of the switch is effected simply by pressing on the module cover rather than by pressing buttons or switches located elsewhere than over the center of the steering wheel. The membrane switch also provides for a conveniently large actuation area.
A problem area with the mounting of membrane switches directly on the airbag module cover is their retention thereon during deployment of the airbag. In U.S. Pat. No. 5,369,232 assigned to the assignee of the present invention, a membrane switch is attached in an illustrative example to the airbag module cover using a standard practice of heat stake retention. This practice involves providing thermoplastic stakes on the rear surface of the module cover which are inserted through complementary openings along the perimeter of a membrane switch assembly. The distal ends of the stakes are heated to form a mushroom type geometry on the end of each stake. Most of the horn switch retention failures experienced with such standard heat staking practice are caused either by the switch slipping over the formed mushroom geometry at the distal end of the stakes or due to the elongation of the stake and switch backing during hot temperature airbag deployment causing the horn switch to separate from the cover as the cover rotates or swivels upon deployment of an airbag or due to the stakes elongating during hot temperature airbag deployment whereby the stakes break in tensile or shear stress.
Accordingly, it is an object of this invention to provide a new and improved method and structure for attaching a horn switch, preferably a membrane horn switch, to a thermoplastic airbag module cover which positively locks the horn switch on the cover and is substantially stronger than standard methods of heat staking a horn switch to the back of an airbag module cover.